Used extensively in cell biology and physiology research to measure intracellular calcium ion (Ca²⁺) concentrations. It functions as a fluorescent indicator that binds calcium with high selectivity, enabling real-time monitoring of calcium dynamics in live cells. When loaded into cells, the compound exhibits a shift in its fluorescence excitation spectrum upon binding Ca²⁺, allowing quantification using fluorescence microscopy, flow cytometry, or spectrofluorometry. Commonly applied in studies involving signal transduction, muscle contraction, neurotransmitter release, and apoptosis. Its pentapotassium salt form improves solubility and cellular uptake, making it suitable for use in physiological buffers and cell-based assays.